1. Field of the Invention
The present invention relates to an epoxy resin composition which gives an excellent cured article without using an additive flame retardant and is excellent in dielectric characteristics, and is also suited for use as a resin composition for semiconductor devices and circuit board devices, and a cured article thereof, a novel epoxy resin used therefore and a production method thereof, and a novel phenol resin as an intermediate of the epoxy resin.
2. Description of the Related Art
An epoxy resin is widely used in the fields of electronics and high functional coating materials because it gives a cured article which causes less shrinkage during curing and is excellent in dimensional stability, electrical insulation properties and chemical resistance. In the field of electronics such as semiconductor encapsulating materials, with the progress of surface mounting of semiconductors and size reduction of semiconductors for the purpose of attaining higher density of electronic components, moisture resistance, particularly solder cracking resistance after subjecting to a moisture resistance test has recently been required strongly to sealing materials. To meet such a requirement, there is known a technique in which the number of aromatic nucleus in the resin is increased and the amount of secondary hydroxyl groups formed during the curing reaction is decreased, and thus moisture resistance of the cured article is improved and stress is reduced. For example, there are proposed an epoxy resin composition in which a solid novolak resin having a reduced functional group concentration obtained by reacting a monostyrenated phenol with formaldehyde or paraformaldehyde is used as a curing agent for epoxy resin (see, for example, Japanese Unexamined Patent Application, First Publication No. H05-132544 (pp. 3-4)) and an epoxy resin composition in which polyglycidyl ether of the solid novolak resin is used (see, for example, Japanese Unexamined Patent Application, First Publication No. H05-140265 (pp. 3-5)). Also there is proposed benzylated polyphenol, which is obtained by modifying polyphenol with a benzylating agent, and thereby a functional group concentration is reduced to improve moisture resistance of the cured article, in particular, to improve package cracking resistance as a surface mounting type semiconductor encapsulating material, and an epoxy resin composition containing the polyglycidyl ether thereof (see, for example, Japanese Unexamined Patent Application, First Publication No. H08-120039 (pp. 4-6)).
The novolak resin, polyphenol, and epoxydated compounds thereof surely have sufficiently low functional group concentration and the resulting cured article is excellent in moisture resistance, and thus obtaining materials which exhibit excellent solder cracking resistance in the fields of electronics and high functional coating materials and can meet the requirement such as lower dielectric constant with recent development of higher-frequency electronic equipments.
However, materials used in the fields of electronics and high functional coating materials must be cope with environmental problems typified by dioxin problem and it has strongly been required to develop a so-called halogen-free flame retardant system in which a resin itself is provided with a flame retardant effect without using a halogen-based additive flame retardant. Although dielectric characteristics are improved in the above-described novolak resin, polyphenol, and epoxydated compounds thereof, since they contain a large amount of flammable pendant-shaped aromatic hydrocarbon groups in the molecular structure, the resulting cured article is inferior in flame retardancy and thus the above-described halogen-free flame retardant system can not be constructed.
Therefore, there has never been obtained an epoxy resin which imparts excellent flame retardancy to the cured article, although it has excellent dielectric characteristics.